1. Field of the Invention
The present invention relates to a system and method for reading semiconductor die information, and more particularly for reading semiconductor die identification information in a parallel test and burn-in system.
2. Description of Prior Art
In some cases semiconductor chips are encoded with an identification (ID), enabling testers to trace individual chips through production. The ID can contain information such as, wafer lot number, wafer number, and coordinates on a wafer. By tracing dies through production and conducting yield studies, manufactures can optimize production of a particular chip.
Often a burn-in test is conducted as part of the production. The purpose of a burn-in procedure is to operate the devices (e.g., SDRAM) for some period of time during which most of the devices subject to infant mortality failure actually fail. The burn-in may include operating the devices under conditions of increased temperature and increased voltage (high current load). These conditions are designed to accelerate the aging process where, for example, a relatively small number of testing hours are equivalent to months of operation. The goal of a burn-in test is to increase the reliability of the devices ultimately marketed.
A test and burn-in system poses unique problems with respect to tracing dies. For example, in order to read burn-in data, a test system needs sufficient memory to capture a serial data stream for each device being tested on a real time basis using a fail memory. In such a system, the expense of the memory is economically undesirable. To this point, no satisfactory method of reading chip ID from a plurality of chips in parallel on a burn-in board is known to be available.
A second problem with tracing dies through burn-in is bus contention. Bus contention can occur when two or more devices attempt to output opposite logic levels on the same or common bus line. In a testing system, during burn-in, drivers and comparators are shared among many devices in parallel to help reduce testing costs. However, to avoid the bus contention that is associated with testing devices in parallel, the devices are tested in banks. Therefore, only one package pin of any device on the common data bus is enabled at any one time.
Therefore a need exists for an efficient system and method for reading semiconductor identification information from a burn-in test board including devices in parallel.
A method according to the present invention is provided for determining memory device identification. The method invokes a serial output from n identification fuses of two or more memory devices, the output for identifying the device, and sampling the serial output every nth bit to determine a fuse state for a fuse of each device. The method repeats the sampling for all n fuses to acquire fuse data for all devices, and determines a pass/fail string corresponding to the sampled output, the pass/fail string being employed to identify the devices through a parallel test and burn-in system.
The output is on an enabled data line which is used during the burn-in test wherein other data lines are disabled for avoiding bus contention. The memory device is a synchronized dynamic random access memory. The fuses are defined as identification fuses prior to invoking the output.
The method also includes storing the pass/fail string for the data in a database, and translating the pass/fail string using a structured query language expression executed against the database. A pass is interpreted as a binary xe2x80x9c1xe2x80x9d and a fail is interpreted as a binary xe2x80x9c0xe2x80x9d. The pass/fail string is a binary data string. The translated pass/fail string is linked to another test. The disabled data lines are tri-state data lines.
According to one embodiment of the present invention, a computer usable medium including computer readable program code embodied therein is provided for causing the computer to determine device identification data. The computer program product includes computer readable program code for causing a computer to invoke a serial output from n identification fuses of a plurality of devices, the output for identifying the devices. The computer program product includes computer readable program code for causing a computer to sample the serial output every nth bit to determine a fuse state for a fuse of each device. Also included is computer readable program code for causing a computer to repeat the sampling for all n fuses to acquire fuse data for all devices. The computer program product further includes computer readable program code for causing a computer to determine a pass/fail string corresponding to the sampled output, the pass/fail string being employed to identify the devices through a parallel test and burn-in system.
The computer readable program code further includes computer readable program code for causing a computer to store the pass/fail expression for the data in a database, and structured query language computer readable program code executed against the database for causing a computer to translate the pass/fail expression.
A system for determining a memory device identification is provided according to an embodiment of the present invention. The system includes a testing board to which memory devices are wired in parallel, each memory device including one or more identification fuses, a strobe, for sampling and comparing the output from the memory devices on an enabled package pin to an expected data, and a memory for storing the results of the comparison.
In addition, the memory includes a first relational database for storing the results against which a structured query language expression is executed for translating the results, and a second relational database including at least one identification field for accepting the translated data string. The memory is an offline memory.